This invention relates to an electroconductive resin composition which is comprised of a thermoplastic fluorine-containing copolymer and carbon black.
Recently demands for electroconductive resins have been increasing in various and widening fields of industry. It has already been revealed that several kinds of organic polymers containing specific dopants exhibit good conductivity. However, practicable electroconductive resins using such polymers are still under development and there is a long distance toward wide purpose applications by solution of technical problems in various aspects. Therefore, electroconductive resins currently on the market are all composite materials obtained by adding conductive fillers to commonly used resins.
The conductivities of conventional electroconductive resins of the composite type cover a wide range. For example, conductive resins having volume resistivity of 10.sup.0 -10.sup.4 .OMEGA..multidot.cm are largely used in plate heaters, radio wave shields, cables, conductive films, etc., while more highly conductive resins having volume resistivity of 10.sup.-3 -10.sup.0 .OMEGA..multidot.cm are used in printed circuits, cell electrode terminals, contacts of electronic calculators, connectors, gaskets, radio wave shields, conductive paints, conductive adhesives, etc.
For conventional electroconductive resins, conductive fillers are selected from carbon black, metal powders and metal fibers with consideration of related factors such as physical properties of the matrix resin, desired conductivity and intended uses of the products. At present carbon black is most widely used as the conductive filler, and it is well known that various degrees of conductivity can be attained by selectively using carbon black of different grades, selecting the matrix resin to which carbon black is added and/or selecting and controlling the process of preparing a conductive resin and shaping it into a desired form.
Polymers useful or considered to be useful for producing conductive resins by combining with carbon black include some fluorine-containing polymers which are known for their excellent resistance to chemicals and weathering as well as good mechanical properties. A typical example of such fluorine-containing polymers is polytetrafluoroethylene (PTFE). There are proposals of electroconductive paints and mouldable conductive resins using a fluorine-containing polymer and carbon black. However, coating films and shaped bodies according to these proposals are generally higher than about 10 .OMEGA..multidot.cm in volume resistivity. To further reduce the resistivity by increasing the amount of carbon black, there arises the need of taking a certain compensating measure such as incorporation of an extra additive for preventing degradation of the mechanical properties of the products.